Phosphor powder, composite, and light-emitting device

ABSTRACT

A phosphor powder composed of α-sialon phosphor particles containing Eu. In a case where an internal quantum efficiency after the phosphor powder is held at 600° C. for 1 hour in an air atmosphere is defined as P1 and an internal quantum efficiency after the phosphor powder is held at 700° C. for 1 hour in an air atmosphere is defined as P2, P1 is equal to or more than 70% and (P1−P2)/P1×100 is equal to or less than 2.8%.

TECHNICAL FIELD

The present invention relates to a phosphor powder, a composite, and alight-emitting device.

BACKGROUND ART

As nitride and oxynitride phosphors, an α-sialon phosphor in which aspecific rare earth element is activated is known to have usefulfluorescence characteristics, and has been applied to a white LED andthe like. The α-sialon phosphor has a structure in which Si—N bonds ofα-silicon nitride crystals are partially substituted with Al—N bonds andAl—O bonds, and specific elements (Ca, Li, Mg, Y, or lanthanide metalsexcept for La and Ce) penetrate into crystal lattices and aresolid-dissolved in order to maintain electrical neutrality. Thefluorescence characteristics are expressed by using some of the elementsthat penetrate into the lattices and are solid-dissolved as a rare earthelement serving as a luminescent center. Among those, the α-sialonphosphor, in which Ca is solid-dissolved and the elements thereof arepartially substituted with Eu, is relatively efficiently excited in awide wavelength range from ultraviolet to blue light and exhibitsemission of yellow to orange light. As an attempt to further improve thefluorescence characteristics of such an α-sialon phosphor, for example,it has been proposed to select an α-sialon phosphor having a specificaverage particle diameter by a classification treatment (Patent Document1).

RELATED DOCUMENT Patent Document

-   [Patent Document 1] Japanese Laid-open Patent Publication No.    2009-96882

SUMMARY OF THE INVENTION Technical Problem

In recent years, a higher brightness of a white LED has been demanded.For example, a further improvement in the light emission characteristicsof a phosphor powder used for the white LED has also been required.

The present invention has been made in view of the problems. An objectof the present invention is to provide a phosphor powder having improvedlight emission characteristics.

Solution to Problem

According to the present invention, there is provided a phosphor powdercomposed of α-sialon phosphor particles containing Eu, in which in acase where an internal quantum efficiency after the phosphor powder isheld at 600° C. for 1 hour in an air atmosphere is defined as P1 and aninternal quantum efficiency after the phosphor powder is held at 700° C.for 1 hour in an air atmosphere is defined as P2, P1 is equal to or morethan 70% and (P1−P2)/P1×100 is equal to or less than 2.8%.

Furthermore, according to the present invention, there is provided acomposite including the above-mentioned phosphor powder and a sealingmaterial that seals the phosphor powder.

In addition, according to the present invention, there is provided alight-emitting device including a light-emitting element that emitsexcitation light, and the above-mentioned composite that converts awavelength of the excitation light.

Advantageous Effects of Invention

According to the present invention, it is possible to provide atechnique relating to a phosphor powder having improved light emissioncharacteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a structure of alight-emitting device according to an embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail.

The phosphor powder according to the embodiment is a phosphor powdercomposed of α-sialon phosphor particles containing Eu. In a case wherean internal quantum efficiency after the phosphor powder is held at 600°C. for 1 hour in an air atmosphere is defined as P1 and an internalquantum efficiency after the phosphor powder is held at 700° C. for 1hour in an air atmosphere is defined as P2, P1 is equal to or more than70% and (P1−P2)/P1×100 is equal to or less than 2.8%.

With the phosphor powder of the present embodiment, it is possible toimprove the fluorescence characteristics of α-sialon phosphor particlesin the related art while holding the excitation wavelength range and thefluorescence wavelength range of the particles. Therefore, as a result,it is possible to improve the light emission characteristics of alight-emitting device using the phosphor powder of the presentembodiment.

Detailed mechanism as a reason therefor is not clear, but is presumed tobe as follows: a phosphor powder, in which P1 is equal to or more than70% and (P1−P2)/P1×100 is equal to or less than 2.8%, has high chemicalstability of the surface, and the elements and compounds that do notcontribute to fluorescence are sufficiently removed. Therefore, it isconsidered that high fluorescence characteristics can be stably obtainedeven in a state of performing no heating.

(α-Sialon Phosphor Particles)

The α-sialon phosphor particles containing Eu are composed of anα-sialon phosphor which will be described below.

The α-sialon phosphor is an α-sialon phosphor containing an Eu element,represented by General Formula: (M1_(x), M2_(y), Eu_(z))(Si_(12−(m+n))Al_(m+n))(O_(n)N_(16−n)) (provided that M1 is a monovalentLi element and M2 are one or more divalent elements selected from thegroup consisting of Mg, Ca, and lanthanide elements (except for La andCe)).

The solid dissolution composition of the α-sialon phosphor is expressedin x, y, and z in the general formula, and m and n determined by anSi/Al ratio and an O/N ratio associated therewith, and satisfies0≤x<2.0, 0≤y<2.0, 0<z≤0.5, 0<x+y, 0.3≤x+y+z≤2.0, 0<m≤4.0, 0<n≤3.0. Inparticular, in a case where Ca is used as M2, the α-sialon phosphor isstabilized in a wide composition range, and by partially substitutingthe elements of Ca with Eu serving as a luminescent center, excitationoccurs by light in a wide wavelength range from ultraviolet to bluelight, whereby a phosphor exhibiting emission of visible light rangingfrom yellow to orange light can be obtained.

In addition, from the viewpoint of obtaining light in bulb color inillumination applications, it is preferable that the α-sialon phosphorincludes no Li or a small amount of L, if any, as the solid dissolutioncomposition. In terms of the general formula, it is preferable tosatisfy 0≤x≤0.1. Furthermore or alternatively, a ratio of Li in theα-sialon phosphor is preferably equal to or more than 0% by mass andequal to or less than 1% by mass.

In general, the α-sialon phosphor has a second crystal phase differentfrom that of the α-sialon phosphor or an amorphous phase which isinevitably present, the solid dissolution composition cannot be strictlydefined by composition analysis or the like. As a crystal phase of theα-sialon phosphor, an α-sialon single phase is preferable, and theα-sialon phosphor may also include aluminum nitride or a polytypoid orthe like thereof as another crystal phase.

In the α-sialon phosphor particles, a plurality of equi-axed primaryparticles are sintered to form aggregated secondary particles. Theprimary particles in the present embodiment refer to the smallestparticles observable with an electron microscope or the like, in whichthe particles can exist singly. The shape of the α-sialon phosphorparticle is not particularly limited. Examples of the shape include aspherical shape, a cubic shape, a columnar shape, and an amorphousshape.

The lower limit of the average particle diameter or the median diameter(D₅₀) of the α-sialon phosphor particles is preferably equal to or morethan 1μ, more preferably equal to or more than 5 μm, and still morepreferably equal to or more than 10 μm. In addition, the upper limit ofthe average particle diameter or the median diameter (D₅₀) of theα-sialon phosphor particles is preferably equal to or less than 30 μm,and more preferably equal to or less than 20 μm. The average particlediameter or the median diameter (D₅₀) of the α-sialon phosphor particlesis a dimension for the secondary particles. By setting the averageparticle diameter or the median diameter (D₅₀) of the α-sialon phosphorparticles to equal to or more than 5 μm, the transparency of thecomposite which will be described later can be further enhanced. On theother hand, by setting the average particle diameter or the mediandiameter (D₅₀) of the α-sialon phosphor particles to equal to or lessthan 30 μm, it is possible to suppress the occurrence of chipping in acase where the composite is cut with a dicer or the like.

Here, the average particle diameter of the α-sialon phosphor particlesmeans a 50% diameter in a volume-based integrated fraction, determinedby a laser diffraction scattering method in accordance with JIS R1629:1997.

Here, the median diameter (D₅₀) of the phosphor powder means a mediandiameter (D₅₀) in a volume-based integrated fraction, determined by alaser diffraction scattering method in accordance with JIS R1629: 1997.

In a case where an internal quantum efficiency after the phosphor powderof the present embodiment is held at 600° C. for 1 hour in an airatmosphere is defined as P1, an internal quantum efficiency after thephosphor powder of the present embodiment is held at 700° C. for 1 hourin an air atmosphere is defined as P2, and an internal quantumefficiency after the phosphor powder of the present embodiment is heldat 800° C. for 1 hour in an air atmosphere is P3, P1 is equal to or morethan 70% and (P1−P2)/P1×100 is equal to or less than 2.8%.

Here, the internal quantum efficiency of the phosphor powder can bemeasured by a spectrophotometer equipped with an integrating sphere.

The internal quantum efficiency after the phosphor powder is held ateach of the above-mentioned temperatures for 1 hour can be regarded asan index of the chemical stability of the surface of the α-sialonphosphor particle. It is considered that as compared with a phosphorpowder in the related art, the phosphor powder of the present embodimenthas extremely high chemical stability of the surface since the indexesdefined by P1 and (P1−P2)/P1×100 satisfy the conditions.

It is more preferable that (P1−P2)/P1×100 is equal to or less than 1.5%.In this manner, it is possible to obtain a phosphor powder having higherchemical stability of the surface.

In the phosphor powder of the present embodiment, it is preferable thatP2 is equal to or more than 68%, in addition to the indexes defined byP1 and (P1−P2)/P1×100 satisfying the conditions. In this manner, it ispossible to further enhance the chemical stability of the surface of theα-sialon phosphor particle.

In addition, in the phosphor powder of the present embodiment, it ispreferable that P3 is equal to or more than 68%, in addition to theconditions. In this manner, it is possible to further enhance thechemical stability of the surface of the α-sialon phosphor particle.

With the phosphor powder described above, it is possible to improve thefluorescence characteristics by satisfying both the condition that P1 isequal to or more than 70% and the condition that (P1−P2)/P1×100 is equalto or less than 2.8%.

(Other Characteristics)

The phosphor powder of the present embodiment preferably satisfies othercharacteristics, in addition to satisfying the above-mentionedcharacteristics relating to P1 and (P1−P2)/P1×100.

As an example of the characteristics, with regard to the phosphorpowder, the ammonium ion concentration C_(A) of the phosphor powder,determined from the following [Extracted Ion Analysis A], is preferablyequal to or more than 15 ppm and 100 ppm, more preferably equal to ormore than 15 ppm and equal to or less than 80 ppm, and still morepreferably equal to or more than 15 ppm and equal to or less than 60ppm.

C_(A) which is within the numerical range is considered to correspondto, in particular, high chemical stability of the surface of thephosphor particle, and the high chemical stability of the surface of thephosphor particle easily enables the mother crystals of the phosphorwhich contributes to fluorescence to be stably present, and therefore,the fluorescence characteristics can be further improved.

[Extracted Ion Analysis A]

0.5 g of phosphor powder is added to 25 ml of distilled water in apolytetrafluoroethylene (PTFE)-made container with a lid, and held at60° C. for 24 hours. Then, the total mass M_(A) of ammonium ionscontained in the aqueous solution from which the solid content has beenremoved by filtration is determined by using an ion chromatographymethod. Then, C_(A) is determined by dividing M_(A) by a mass of thephosphor powder. That is, C_(A) is an index indicating the amount ofammonium ions per unit mass of the phosphor powder (solid).

For supplementary explanation, M_(A) can be determined by multiplyingthe ammonium ion concentration of the aqueous solution measured by theion chromatography method by the mass (25 g) of water used.

In addition, C_(A) is determined by dividing M_(A) by the mass (0.5 g)of the phosphor powder provided for the analysis.

In a case where the unit of M_(A) is “gram (g)”, C_(A) [unit: ppm] canbe determined by dividing M_(A) [unit: g] by the mass (0.5 g) of thephosphor powder and multiplying the calculated value by 10⁶.

As another example of the characteristics, the diffuse reflectance ofthe phosphor powder with respect to light at a wavelength of 600 nm ispreferably equal to or more than 93 and equal to or less than 99%, andmore preferably equal to or more than 94% and equal to or less than 96%.The diffuse reflectance can be measured by an ultraviolet-visiblespectrophotometer equipped with an integrating sphere device. Withregard to a method for measuring the diffuse reflectance, refer toExamples which will be described later.

The diffuse reflectance is an index indicating a degree of diffusereflection of light. That is, the diffuse reflectance can be related tothe surface condition of a phosphor particle, the particle diameter ofthe phosphor particle, the particle size distribution of a phosphorpowder, and the like. Although the details are unknown, it is presumedthat the diffuse reflectance of the phosphor powder with respect tolight at a wavelength of 600 nm which is within the numerical rangeindicates, for example, that a heterogeneous phase not contributing tofluorescence is sufficiently removed from the surface of the phosphorparticle.

In the present embodiment, particularly from the viewpoints of goodfluorescence characteristics (luminous efficiency and the like), it ispreferable that the median diameter D₅₀ of the phosphor powder is equalto or more than 10 μm and equal to or less than 20 μm, and the diffusereflectance with respect to light at a wavelength of 600 nm is withinthe numerical range.

(Method for Producing Phosphor Powder)

A method for producing a phosphor powder composed of the α-sialonphosphor particles of the present embodiment will be described. In theα-sialon phosphor particles, a part of a raw material powder mainlyundergoes a reaction to form a liquid phase, and each of the elementsmoves through the liquid phase in the synthesis process, wherebyformation of a solid solution and grain growth proceed.

First, the raw materials including the elements constituting theα-sialon phosphor particles containing Eu are mixed. Calcium issolid-dissolved at a high concentration in the α-sialon phosphorparticles having a low oxygen content, which have been synthesized usingcalcium nitride as a calcium raw material. In particular, in a casewhere the Ca solid dissolution concentration is high, it is possible toobtain a phosphor having a light emission peak wavelength on a higherwavelength side (equal to or more than 590 nm, more specifically equalto or more than 590 nm and equal to or less than 610 nm, and still morespecifically equal to or more than 592 nm and equal to or less than 608nm) than a composition in the related art, using an oxide raw material.Specifically, in the general formula, it is preferable to satisfy1.5<x+y+z≤2.0. It is also possible to finely tune the emission spectrumby partially substituting the elements of Ca with Li, Mg, Sr, Ba, Y, andlanthanide elements (except for La and Ce).

Examples of a raw material powder other than those include siliconnitride, aluminum nitride, and an Eu compound. Examples of the Eucompound include europium oxide, a compound that turns into europiumoxide after heating, and europium nitride. Europium nitride, which canreduce the amount of oxygen in the system, is preferable.

In a case where an appropriate amount of the α-sialon phosphor particlespreviously synthesized is added to a raw material powder, this additioncan serve as a base point of the grain growth to obtain α-sialonphosphor particles having relatively short-axis diameters, and theparticle shapes can be controlled by changing the forms of the α-sialonparticles to be added.

Examples of a method of mixing the above-mentioned respective rawmaterials include a dry mixing method and a method in which wet mixingis performed in an inert solvent that does not substantially react withthe respective components of the raw materials, and then the solvent isremoved. Examples of a mixing device include a V type mixer, a rockingmixer, a ball mill, and a vibrating mill. Mixing of calcium nitridewhich is unstable in the atmosphere is preferably performed in a glovebox in an inert atmosphere since the hydrolysis and the oxidation of thesubstance give an influence on the characteristics of a syntheticproduct.

A container made of a material having a low reactivity with a rawmaterial and a phosphor to be synthesized, for example, a container madeof boron nitride is filled with a powder obtained by mixing (hereinaftersimply referred to as a raw material powder). Then, the powder is heatedfor a predetermined time in a nitrogen atmosphere. In this manner, anα-sialon phosphor can be obtained. A temperature for the heat treatmentis preferably equal to or higher than 1,650° C. and equal to or lowerthan 1,950° C.

By setting the temperature for the heat treatment to equal to or higherthan 1,650° C., it is possible to reduce the amount of residualunreacted products and make the primary particles sufficiently grow. Inaddition, by setting the temperature to equal to or lower than 1,950°C., it is possible to suppress remarkable sintering between theparticles.

From the viewpoint of suppressing sintering between the particles duringthe heating, it is preferable that the container is filled with anincreased volume of the raw material powder. Specifically, it ispreferable that a bulk density at the time of filling the raw materialpowder in the container is set to equal to or less than 0.6 g/cm³.

The heating time for the heat treatment is preferably equal to or morethan 2 hours and equal to or less than 24 hours in terms of a time rangeduring which there are no inconveniences such as presence of a largeamount of residual unreacted substances, insufficient growth of primaryparticles, and sintering between the particles.

In the above-mentioned step, an α-sialon phosphor having an ingot-shapedouter form is produced. By subjecting this ingot-shaped α-sialonphosphor to a pulverizing step in which the phosphor is pulverized by apulverizer such as a crusher, a mortar pulverizer, a ball mill, avibrating mill, and a jet mill, and a sieve classification step aftersuch the pulverizing treatment, it is possible to obtain a phosphorpowder composed of α-sialon phosphor particles having an adjusted D₅₀particle diameter of secondary particles. In addition, it is possible toadjust the D₅₀ particle diameter of the secondary particles byperforming a step in which the phosphor powder is dispersed in anaqueous solution to remove the secondary particles which have smallparticle diameters and are hardly settled.

The phosphor powder composed of the α-sialon phosphor particlesaccording to the embodiment can be manufactured by carrying out theabove-mentioned steps and then carrying out an acid treatment step.

In the acid treatment step, for example, the α-sialon phosphor particlesare immersed in an acidic aqueous solution. Examples of the acidicaqueous solution include an acidic aqueous solution including one kindof acid selected from acids such as hydrofluoric acid, nitric acid, andhydrochloric acid, and an aqueous mixed acid solution obtained by mixingtwo or more kinds of the acids. Among these, an aqueous hydrofluoricacid solution including hydrofluoric acid alone and an aqueous mixedacid solution obtained by mixing hydrofluoric acid and nitric acid aremore preferable. The stock solution concentration of the acidic aqueoussolution is appropriately set depending on the strength of an acid used,but is, for example, preferably equal to or more than 0.7% and equal toor less than 100%, and more preferably equal to or more than 0.7% andequal to or less than 40%. In addition, a temperature at which the acidtreatment is carried out is preferably equal to or higher than 25° C.and equal to or lower than 90° C., and more preferably equal to orhigher than 60° C. and equal to or lower than 90° C., and the reactiontime (immersion time) is preferably equal to or more than 15 minutes andequal to or less than 80 minutes.

Preferred aspects of the acid treatment step include an aspect in whichthe phosphor powder is added to an acidic solution and then the mixtureis stirred for a certain period of time. In this manner, a reaction withthe acid can proceed more reliably on the surface of the α-sialonphosphor particle. By performing the stirring at a high speed, the acidtreatment on the particle surface is likely to be sufficientlyperformed. The term “high speed” as used herein depends on a stirringdevice used, but in a case where a laboratory-level magnetic stirrer isused, the stirring speed is, for example, equal to or more than 400 rpm,and in reality, equal to or more than 400 rpm and equal to or less than500 rpm. For the purpose of normal stirring, which is to constantlysupply a new acid to the particle surface, a stirring speed ofapproximately 200 rpm is sufficient, but by performing the stirring at ahigh speed of equal to or more than 400 rpm, the elements and compoundsnot contributing to fluorescence are sufficiently removed and/or thechemical stability of the particle surface is enhanced due to a physicalaction in addition to a chemical action.

The conditions that P1 is equal to or more than 70% and (P1−P2)/P1×100is equal to or less than 2.8%, each defined for the internal quantumefficiency after the heat treatment, as mentioned above, can becontrolled by optimally adjusting the stock solution concentration of anacidic aqueous solution used for an acid treatment, a temperature at thetime of the acid treatment, a reaction time, a stirring speed, and thelike. For example, by adopting conditions which approximate to acombination of the stock solution concentration of an acidic aqueoussolution, a temperature during an acid treatment, a reaction time, and astirring speed, with reference to abundant Examples which will bedescribed below, thus to carry out the acid treatment, it is possible toadjust P1 and (P1−P2)/P1×100 of the phosphor powder to desired values.

(Composite)

The composite according to an embodiment includes the above-mentionedphosphor particles and a sealing material that seals the phosphorparticles. In the composite according to the present embodiment, aplurality of the above-mentioned phosphor particles are dispersed in thesealing material. As the sealing material, a well-known material such asa resin, a glass, and ceramics can be used. Examples of the resin usedfor the sealing material include transparent resins such as a siliconeresin, an epoxy resin, and a urethane resin.

Examples of a method for manufacturing the composite include amanufacturing method in which a powder composed of α-sialon phosphorparticles of the present embodiment is added to a liquid resin, apowdered glass, or ceramics, and the mixture is mixed uniformly, andthen cured or sintered by a heat treatment.

(Light-Emitting Device)

FIG. 1 is a schematic cross-sectional view showing a structure of alight-emitting device according to the present embodiment. As shown inFIG. 1, a light-emitting device 100 includes a light-emitting element120, a heat sink 130, a case 140, a first lead frame 150, a second leadframe 160, a bonding wire 170, a bonding wire 172, and a composite 40.

The light-emitting element 120 is mounted in a predetermined region onthe upper surface of the heat sink 130. By mounting the light-emittingelement 120 on the heat sink 130, the heat dissipation of thelight-emitting element 120 can be enhanced. Further, a packagingsubstrate may be used instead of the heat sink 130.

The light-emitting element 120 is a semiconductor element that emitsexcitation light. As the light-emitting element 120, for example, an LEDchip that generates light at a wavelength of equal to or more than 300nm and equal to or less than 500 nm, corresponding to near-ultravioletto blue light, can be used. One electrode (not shown in the drawings)arranged on the upper surface side of the light-emitting element 120 isconnected to the surface of the first lead frame 150 through the bondingwire 170 such as a gold wire. In addition, the other electrode (notshown in the drawings) formed on the upper surface of the light-emittingelement 120 is connected to the surface of the second lead frame 160through the bonding wire 172 such as a gold wire.

In the case 140, a substantially funnel-shaped recess whose holediameter gradually increases toward the upside from the bottom surfaceis formed. The light-emitting element 120 is provided on the bottomsurface of the recess. The wall surface of the recess surrounding thelight-emitting element 120 serves as a reflective plate.

The recess whose wall surface is formed by the case 140 is filled withthe composite 40. The composite 40 is a wavelength conversion memberthat converts excitation light emitted from the light-emitting element120 into light at a longer wavelength. The composite of the presentembodiment is used as the composite 40, and α-sialon phosphor particles1 of the present embodiment are dispersed in a sealing material 30 suchas a resin. The light-emitting device 100 emits a mixed color of lightof the light-emitting element 120 and light generated from the α-sialonphosphor particles 1 which are excited by absorbing the light of thelight-emitting element 120. The light-emitting device 100 preferablyemits white light by the mixed color of the light of the light-emittingelement 120 and the light generated from the α-sialon phosphor particles1.

In the light-emitting device 100 of the present embodiment, by settingP1 to equal to or more than 70% and setting (P1−P2)/P1×100 to equal toor less than 2.8% in a case where an internal quantum efficiency after aphosphor powder composed of the α-sialon phosphor particles 1 is held at600° C. for 1 hour in an air atmosphere is defined as P1 and an internalquantum efficiency after the phosphor powder is held at 700° C. for 1hour in an air atmosphere is defined as P2 as mentioned above, thefluorescence characteristics of the α-sialon phosphor particles 1 andthe composite 40 can be improved, and the light emission intensity ofthe light-emitting device 100 can be improved.

In FIG. 1, a surface mounting type light-emitting device is illustrated,but the light-emitting device is not limited to the surface mountingtype device. The light-emitting device may be of a cannonball type, achip-on-board (COB) type, or a chip-scale-package (CSP) type.

The embodiments of the present invention have been described above, butthese are examples of the present invention and various configurationsother than the examples can also be adopted.

EXAMPLES

Hereinafter, the present invention will be described with reference toExamples and Comparative Examples, but the present invention is notlimited thereto.

Example 1

In a glove box, 62.4 parts by mass of a silicon nitride powder(manufactured by Ube Kosan Co., Ltd., E10 grade), 22.5 parts by mass ofan aluminum nitride powder (manufactured by Tokuyama Corporation, Egrade), 2.2 parts by mass of an europium oxide powder (manufactured byShin-Etsu Chemical Co., Ltd., RU grade), and 12.9 parts by mass of acalcium nitride powder (manufactured by Kojundo Chemical Lab. Co., Ltd.)were used as a blend composition of a raw material powder, and the rawmaterial powders were dry-blended and then passed through a nylon-madesieve having a mesh size of 250 μm to obtain a raw material mixedpowder. A cylindrical boron nitride-made container (manufactured byDenka Co., Ltd., N-1 grade) with a lid, having an internal volume of 0.4liters, is filled with 120 g of the raw material mixed powder.

This raw material mixed powder was subjected to a heat treatment at1,800° C. for 16 hours in a nitrogen atmosphere at an atmosphericpressure in an electric furnace of a carbon heater together with acontainer. Since calcium nitride included in the raw material mixedpowder was easily hydrolyzed in the air, the boron nitride-madecontainer filled with the raw material mixed powder was immediately setin the electric furnace rapidly after being taken out from the glovebox, and immediately evacuated to a vacuum to prevent a reaction ofcalcium nitride.

The synthetic product was lightly crushed in a mortar and passed througha sieve having a mesh size of 150 μm to obtain a phosphor powder. Withregard to this phosphor powder, the crystal phase was examined by powderX-ray diffraction measurement (X-ray Diffraction, hereinafter referredto as XRD measurement) using CuKα rays, and thus, the existing crystalphase was a Ca-α-sialon (α-sialon including Ca) containing an Euelement.

Next, 3.2 ml of 50% hydrofluoric acid and 0.8 ml of 70% nitric acid weremixed to obtain a mixed stock solution. 396 ml of distilled water wasadded to the mixed stock solution, and the concentration of the mixedstock solution was diluted to 1.0% to prepare 400 ml of an aqueous mixedacid solution. 30 g of a phosphor powder composed of the above-mentionedα-sialon phosphor particles was added to the aqueous mixed acidsolution, the temperature of the aqueous mixed acid solution was kept at80° C. in a beaker with a capacity of 500 ml, and the aqueous mixed acidsolution was subjected to an acid treatment in which the aqueous mixedacid solution was immersed for 30 minutes under stirring at a rotationspeed of 450 rpm using a magnetic stirrer. The powder after the acidtreatment was thoroughly washed with distilled water, filtered, dried,and then passed through a sieve having a mesh size of 45 μm tomanufacture a phosphor powder composed of the α-sialon phosphorparticles of Example 1.

Example 2

A phosphor powder composed of α-sialon phosphor particles of Example 2was manufactured by the same procedure as in Example 1, except that anaqueous mixed acid solution having a stock solution concentration of1.0% was prepared by adding 396 ml of distilled water to a mixed stocksolution obtained by mixing 1.2 ml of 50% hydrofluoric acid and 2.8 mlof 70% nitric acid, instead of the aqueous mixed acid solution used inExample 1.

Example 3

A phosphor powder composed of α-sialon phosphor particles of Example 3was manufactured by the same procedure as in Example 1, except that anaqueous mixed acid solution having a stock solution concentration of5.0% was prepared by adding 380 ml of distilled water to a mixed stocksolution obtained by mixing 10 ml of 50% hydrofluoric acid and 10 ml of70% nitric acid, instead of the aqueous mixed acid solution used inExample 1, and the phosphor powder was immersed for 30 minutes while thetemperature of the aqueous mixed acid solution was kept at 30° C.

Example 4

A phosphor powder composed of α-sialon phosphor particles of Example 4was manufactured by the same procedure as in Example 1, except that anaqueous mixed acid solution having a stock solution concentration of 25%was prepared by adding 300 ml of distilled water to a mixed stocksolution obtained by mixing 50 ml of 50% hydrofluoric acid and 50 ml of70% nitric acid, instead of the aqueous mixed acid solution used inExample 1, and the phosphor powder was immersed for 60 minutes while thetemperature of the aqueous mixed acid solution was kept at 80° C.

Comparative Example 1

A phosphor powder composed of α-sialon phosphor particles of ComparativeExample 1 was manufactured by the same procedure as in Example 1, exceptthat an aqueous mixed acid solution having a stock solutionconcentration of 0.5% was used by adding 398 ml of distilled water to amixed stock solution obtained by mixing 1.0 ml of 50% hydrofluoric acidand 1.0 ml of 70% nitric acid, instead of the aqueous mixed acidsolution used in Example 1, the temperature of the aqueous mixed acidsolution was kept at 80° C. in a beaker with a capacity of 500 ml, andthe aqueous mixed acid solution was subjected to an acid treatment inwhich the aqueous mixed acid solution was immersed for 30 minutes understirring at a rotation speed of 300 rpm using a magnetic stirrer.

The stock solution concentration of the aqueous mixed acid solution andthe stirring rotation speed adopted in Comparative Example 1 were set tothe levels which had been normally used in the related art.

(Measurement of Particle Size)

A particle size was measured by a laser diffraction scattering method inaccordance with JIS R1629: 1997, using Microtrac MT3300EX II(MicrotracBEL Corporation). 0.5 g of a phosphor powder was put into 100cc of ion exchange water, the mixture was subjected to a dispersiontreatment with Ultrasonic Homogenizer US-150E (Nissei Corporation, chipsize: φ20, Amplitude: 100%, oscillation frequency: 19.5 KHz, amplitudeof vibration: about 31 μm) for 3 minutes, and then the particle size wasmeasured with MT3300EX II. The median diameter (D₅₀) was determined fromthe obtained particle size distribution.

(Light Emission Characteristics)

With regard to each of the obtained phosphor powders, the internalquantum efficiency and the external quantum efficiency at roomtemperature were measured by a spectrophotometer (MCPD-7000 manufacturedby Otsuka Electronics Co., Ltd.) and calculated by the followingprocedure.

The phosphor powder was filled so that the surface of a recess cell wassmooth, and an integrating sphere was attached. Monochromatic lightspectrally split into a wavelength of 455 nm from a light emissionsource (Xe lamp) was introduced into the integrating sphere using anoptical fiber. A sample of the phosphor powder was irradiated with themonochromatic light as an excitation source, and measurement of thefluorescence spectrum of the sample was performed.

A standard reflective plate (Spectralon manufactured by Labsphere Inc.)having a reflectance of 99% was attached to a sample unit, and thespectrum of excitation light at a wavelength of 455 nm was measured. Atthat time, the number (Qex) of excitation light photons was calculatedfrom a spectrum in the wavelength range of equal to or more than 450 nmand equal to or less than 465 nm.

A phosphor powder composed of the α-sialon phosphor particles wasattached to the sample unit, and the number (Qref) of reflectedexcitation light photons and the number (Qem) of fluorescent lightphotons were calculated. The number of reflected excitation lightphotons was calculated in the same wavelength range as the number ofexcitation light photons, and the number of fluorescent light photonswas calculated in the range of equal to or more than 465 nm and equal toor less than 800 nm.Internal quantum efficiency=(Qem/(Qex−Qref))×100External quantum efficiency=(Qem/Qex)×100

In a case where the standard sample NSG1301 sold by Sialon Co., Ltd. wasmeasured using the measurement method, the external quantum efficiencywas 55.6% and the internal quantum efficiency was 74.8%. The device wascalibrated using this sample as a standard.

In addition, the internal quantum efficiencies after heat treatmentsunder the following three conditions were each independently measured.

(1) After the phosphor powder is held at 600° C. for 1 hour, theinternal quantum efficiency P1 is measured.

(2) After the phosphor powder is held at 700° C. for 1 hour, theinternal quantum efficiency P2 is measured.

(3) After the phosphor powder is held at 800° C. for 1 hour, theinternal quantum efficiency P3 is measured.

The conditions for each heat treatment are listed below.

-   -   High-temperature atmosphere furnace (under air atmosphere)    -   Sample holding method: Sealing type (holding a sample in an        alumina container with a lid, having an internal volume of 30        cc)

(P1−P2)/P1×100(%) was calculated using the obtained P1 and P2. Theresults obtained for the internal quantum efficiency and the externalquantum efficiency are shown in Table 1.

Incidentally, the peak wavelength of the emission spectrum of thephosphor powder obtained by the measurement (excitation lightwavelength: 455 nm) was 600 nm (a relatively high wavelength) inExamples 1 to 4.

(Measurement of Ammonium Ion Concentration C_(A) in Phosphor Powder)

With regard to the phosphor powder of Example 2, the ammonium ionconcentration C_(A) was measured by the following procedure.

0.5 g of a phosphor powder was added to 25 ml of distilled water in aPTFE container with a lid. The container into which the phosphor powderand distilled water had been put was held at 60° C. for 24 hours, andthen the solid content was removed by filtration. The ammonium ionconcentration in the aqueous solution from which the solid content hadbeen removed was measured by an ion chromatography device (manufacturedby Thermo Fisher Scientific Inc.), and the total mass M_(A) (unit: g) ofthe eluted ammonium ions was calculated. Then, M_(A) was divided by themass (0.5 g) of the phosphor powder and multiplied by 10⁶ to determinean ammonium ion concentration C_(A) (unit: ppm) of the phosphor powder.

(Measurement of Diffuse Reflectance of Phosphor Powder)

With regard to the phosphor powder of Example 2, the diffuse reflectanceat a wavelength of 600 nm was measured as follows.

The diffuse reflectance was measured by attaching an integrating spheredevice (ISV-722) to an ultraviolet-visible spectrophotometer (V-650)manufactured by JASCO Corporation. Baseline correction was performedwith a standard reflective plate (Spectralon), a solid sample holderfilled with the phosphor powder was attached, and the diffusereflectance with respect to light at a wavelength of 600 nm wasmeasured.

Various types of information with regard to Examples and ComparativeExamples are shown in Table 1.

Although not shown in Table 1, the ammonium ion concentration C_(A) ofthe phosphor powder of Example 2 was 29 ppm. In addition, the diffusereflectance at a wavelength of 600 nm of the phosphor powder of Example2 was 94.8%.

TABLE 1 Example Example Example Example Comparative 1 2 3 4 Example 1Acid treatment Acid solution 50% Hydrofluoric acid (ml) 3.2 1.2 10 501.0 70% Nitric acid (ml) 0.8 2.8 10 50 1.0 Liquid ratio (amount of 8:23:7 5:5 5:5 5:5 hydrofluoric acid: amount of nitric acid) Distilledwater (ml) 396 396 380 300 398 Stock solution 1.0 1.0 5.0 25 0.5concentration (%) Reaction Temperature (° C.) 80 80 30 80 80 conditionsTime (min) 30 30 30 60 30 Stirring speed (rpm) 450 450 450 450 300Particle size D₅₀ (μm) 15.6 14.5 14.8 16.3 15.6 Internal quantumefficiency P1 (%) after 1 hour at 600° C. 78.0 78.0 79.0 76.3 66.5Internal quantum efficiency P2 (%) after 1 hour at 700° C. 76.0 78.078.0 75.6 64.6 Internal quantum efficiency P2 (%) after 1 hour at 800°C. 75.0 75.0 76.0 72.5 64.6 (P1-P2)/81 × 100 (%) 2.6 0.0 1.3 0.9 2.9Light emission Internal quantum efficiency (%) 79.9 80.3 80.2 77.1 73.7characteristics External quantum efficiency (%) 71.0 71.0 71.3 67.6 65.7

As shown in Table 1, it was confirmed that the phosphor powder ofExamples 1 to 4 satisfying the conditions that P1 was equal to or morethan 70% and (P1−P2)/P1×100 was equal to or less than 2.8% hadimprovements in both the internal quantum efficiency and the externalquantum efficiency, as compared with Comparative Example 1 notsatisfying the condition.

Additional Comparative Example: Example in which Acid TreatmentCondition was Changed in Example 2

A phosphor powder composed of the α-sialon phosphor particles wasobtained in the same manner as in Example 2, except that the stirringspeed by the magnetic stirrer during the acid treatment was changed from450 rpm to 200 rpm which was a normal level.

With regard to the phosphor powder obtained in this AdditionalComparative Example, the median diameter D₅₀ was 14.5 μm, the diffusereflectance at a wavelength of 600 nm was 93.5%, and the ammonium ionconcentration C_(A) of the phosphor powder was 113 ppm.

In addition, with regard to the phosphor powder obtained in AdditionalComparative Example, the internal quantum efficiency was 75.4% and theexternal quantum efficiency was 66.6%, which were the results inferiorto the levels of Example 2 (and other Examples).

From the results of Additional Comparative Example, and the like, it isunderstood that:

-   -   the final phosphor powder is different between the case of the        “high-speed stirring” in which the stirring speed in the acid        treatment is 450 rpm (Example 2) and the case of the “low-speed        stirring” in which the stirring speed in the acid treatment is        200 rpm, and    -   the phosphor powder obtained by the low-speed stirring is        deteriorated in light emission characteristics.

This application claims priority based on Japanese Application JapanesePatent Application No. 2019-069109 filed on Mar. 29, 2019, thedisclosures of which are incorporated herein by reference in theirentireties.

REFERENCE SIGNS LIST

-   1: α-sialon phosphor particle-   30: sealing material-   40: composite-   100: light-emitting device-   120: light-emitting element-   130: heat sink-   140: case-   150: first lead frame-   160: second lead frame-   170: bonding wire-   172: bonding wire

The invention claimed is:
 1. A phosphor powder composed of α-sialonphosphor particles containing Eu, wherein the α-sialon phosphorparticles are composed of an α-sialon phosphor containing an Eu element,represented by General Formula: (M1_(x), M2_(y),Eu_(z))(Si_(12−(m+n))Al_(m+n))(O_(n)N_(16−n)) (provided that M1 is amonovalent Li element and M2 is a divalent Ca element), and in thegeneral formula, x=0, 0<y<2.0, 0<z≤0.5, 0<x+y, 0.3≤x+y+z≤2.0, 0<m≤4.0,and 0<n≤3.0 are satisfied, and in a case where an internal quantumefficiency after the phosphor powder is held at 600° C. for 1 hour in anair atmosphere is defined as P1 and an internal quantum efficiency afterthe phosphor powder is held at 700° C. for 1 hour in an air atmosphereis defined as P2, P1 is equal to or more than 70% and (P1−P2)/P1×100 isequal to or less than 2.8%.
 2. The phosphor powder according to claim 1,wherein the internal quantum efficiency P2 is equal to or more than 68%.3. The phosphor powder according to claim 1, wherein an internal quantumefficiency P3 after the phosphor powder is held at 800° C. for 1 hour isequal to or more than 68%.
 4. A composite comprising: the phosphorpowder according to claim 1; and a sealing material that seals thephosphor powder.
 5. A light-emitting device comprising: a light-emittingelement that emits excitation light; and the composite according toclaim 4, that converts a wavelength of the excitation light.